Deepwater DST Planning and Operations From a DP Vessel

Abstract

Abstract ConocoPhillips (COPC) is developing the Magnolia field with a Tension Leg Platform (TLP) in 4674 feet of water at Garden Banks (GB) block 783 in the Gulf of Mexico (GOM). The field was discovered in 1999 and appraisal wells were drilled in 2000 and 2001. Field development approval was obtained in 2001. The approved depletion plan and well construction strategy included drilling and casing wells prior to the installation of the TLP (pre-drilling), pre-completing and testing one well during the pre-drilling program, and completing the remaining wells from a completion rig installed on the TLP. The GB783 A2ST3BP1 well was successfully drill-stem tested (DST) from the Ensco 7500 dynamically positioned (DP) semi-submersible drilling vessel in June 2003 as part of the Magnolia field development. The pre-completion and DST operations overcame a number of challenges which included the frac-packing of a thick, fine-grained interval, and well testing from a DP semi-submersible drilling rig while simultaneously transferring produced hydrocarbons to a transportation barge moored to the rig. The objectives of the pre-completion/DST were to plan and execute the operations safely, validate the sand control design, determine well performance and reservoir properties, and verify the effectiveness of the completion procedures prior to the TLP rig completion program. This paper will focus on the extensive planning process and the operational aspects of performing a DST in a deepwater environment. Introduction The Magnolia field is located in GB 783 in the GOM. The field location is shown in Figure 1. The Magnolia asset team was formed in 2001 prior to the drilling of the last appraisal well. Front end loading (FEL) leading up to field sanction in December 2001 included concept selection and field development plans. The Magnolia field will be developed from a TLP to provide direct vertical access (DVA) for recompletions, future sidetrack drilling, flow assurance and cost effective remediation. The Magnolia development will be the fourth TLP project developed and operated by ConocoPhillips, utilizing experience from the Hutton, Jolliet and Heidrun TLP's. The Magnolia development wells were pre-drilled; i.e., the drilling operations were conducted from a mobile offshore drilling unit while the TLP was being fabricated. The advantages of pre-drilling included:minimizing capital exposure risks until shallow water flow sands are isolated,allowing TLP well operations to be conducted with a lighter, lower cost completion rig which would further reduce the size and cost of the TLP hull,additional reservoir characterization prior to the TLP installation,accelerating plateau production, andtesting completion techniques in the pre-completed well prior to the "batch" completions of the remaining wells. Detailed engineering and drilling services procurement were conducted in 2002 just after project sanction. Prior to contracting a DP drilling vessel for the pre-drilling program, a hazardous operation (HAZOP) and quantitative risk analysis were performed with drilling, completion and service company personnel to determine the feasibility of using a DP rig for the pre-completion and DST operations. The results of the study indicated that a DP rig would be acceptable, and the Ensco 7500 semi-submersible rig was contracted for the program. The well selected for the pre-completion/DST was the A2ST3BP1. This operation was the first DST to simultaneously transfer oil from a DP rig to a moored barge during a well test. Following the TLP installation, a completion rig will be utilized on the Magnolia TLP to complete the pre-drilled wells. The upper completion equipment will be installed in the pre-completed A2ST3BP1 well after the production riser is installed using the TLP completion rig.